All right, I've been thinking about this a lot and I've done some research. It's no secret that JK 'borrows' from ancient legends and Arthurian themes seem to be a favorite. With that in mind I give you this:
Aren't there four Horcurxes left?
Also, when I hear Hallows I think All Hallows Eve - the time when the veil between worlds is easily parted and the spirits of the dead return. Perhaps the veil at the Dept. of Mysteries will play a part in the storyline? JK has stated that we will learn more about ghosts... Maybe Sirius or Dumbledore (or both) will come back as one? Alright, that's prolly just wishful thinking, but still....